Serrated-shaft connection

ABSTRACT

A serrated-shaft connection between a shaft (1) and a hub (4) has a large number of teeth (2, 5) that are located on the outer circumferential surface of the shaft (1) and the inner circumferential surface of the hub (4), respectively. The profiles (6) of the teeth (5) of the hub (4) are bent convexly in cross section. In such a connection, it is essential that the profiles (3, 6) of the teeth (2, 5) of the shaft (1) and the hub (4) should be bent differently in such a way that the profiles (3) of the teeth (2) of the shaft (1) will have distances above the top of the teeth that are different from those above the top of the teeth (5) of the hub (4). As a result, the tooth profiles of the shaft and the hub can mesh with each other during assembly so that a compressive connection that fits with great precision is obtained.

BACKGROUND OF THE INVENTION

The invention is concerned with a serrated-shaft connection between ashaft and a hub with a large number of teeth that are located on theouter circumference of the shaft and on the inner circumference of thehub.

BRIEF DESCRIPTION OF THE PRIOR ART

In known toothed-shaft connections of this kind, the tooth profiles ofthe teeth of the shaft and the hub are made so that they are alwaysequidistant or nearly equidistant from each other in the meshing zone.In such devices, the tooth profiles or edges are made in straight linesor are involuted in cross section, for example.

If such a known serrated-shaft connection is used in a compressiveconnection, no uniform compression can be achieved because of the usualtoothing deviations. Instead, play or compression that is too highappears in the tolerance limit areas. If there is too much play betweenthe teeth of the shaft and the hub, "frictional corrosion" forms and theconnection works loose. If there is too little play--that is, if thecompression is too great--the hub becomes locally overelongated. Thisresults in difficulties, for example, when the serrated-shaft connectionis used for fastening a detent to a shaft of a vehicle's gear box,because the connection is too loose or the detent's exterior toothing isstretched. Depending upon its cross section, the exterior toothing ofthe detent also goes partially out of round, which makes assembly andoperation of the transmission much harder.

SUMMARY OF THE INVENTION

The object of the invention is to improve the precision of thesynchronization of a known serrated-shaft connection without reducingits manufacturing tolerance.

That object is achieved by having the profiles or edges of the shaftteeth and the hub teeth bent differently in such a way that the profilesof the shaft teeth have distances above the top of the teeth that aredifferent from those above the top of the hub teeth.

Owing to the construction of the tooth profiles according to theinvention, the compression of the sides can be favorably influenced byselecting an appropriate size and method of securing the bent toothflank in place and by selecting appropriate materials. Thus,discrepencies of tooth flank shape can be harmlessly compensated anddeviations of tooth flank direction and spacing can be compensated forsince the defective places resulting from overstraining of material canyield. As a result, the tooth profiles of the shaft and the hub can fiteach other. The space between the teeth in the bottom of the hub becomeswider than before without modification of the profile. As a result,improper meshing with the shaft is prevented, and the serrated-shaftconnection can be constructed more easily.

If a shaft with conventional toothing is used--with involuted profile,for example--it is advantageous if the tooth profiles of the hub's teethare bent convexly in cross section. In this case, two convexly benttooth profiles that can fit each other always meet each other.

The shape of the bent portion of the tooth profiles can be very simplyproduced geometrically as a section of an arc.

The midpoint of the bent portion of the tooth profiles of the hub teethlies on the normal line that runs through the point of contact betweenthe tooth profiles of the shaft and the hub. If a measuring device isused for indirect checking of the hub teeth's thickness and themeasuring device is made of such a size that its midpoint also lies onthe normal line, a precise equalization of the thickness of the hubteeth with the thickness of the shaft teeth is possible because thepoint of contact between the measuring device and the hub tooth profilecoincides with the point of contact between the shaft tooth profile andhub tooth profile.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be explained in greater detail with the help ofan embodiment that is represented in the accompanying drawing, in which;

FIG. 1 shows a partial cross section through the serrated-shaftconnection according to the invention; and

FIG. 2 shows a variation of the bent portion of the tooth profile ofFIG. 1.

DETAILED DESCRIPTION

A shaft 1 carries teeth 2 on its outer circumferential surface whoseflanks or sides 3 have the shape of an involute, for example.

A hub 4 has teeth 5 on its inner circumferential surface. The profiles 6of the teeth 5 of the hub 4 have a convexly bent shape in cross section.If the hub's toothing is produced by broaching, sintering or anothershaping process, for example, it is advantageous if the bent portion ofthe tooth profiles 6 is either a section of an arc or has at least onepoint of discontinuity. Thus, the convex bent portion has a break atleast one point, as is shown in FIG. 2. If the toothing of the hub 4 isproduced by a rotary-furnace process, on the other hand, it issufficient (in accordance with rolling kinematics) for the bent portionof the tooth profiles 6 to be approximately a section of an arc. Thearc-shaped section of the tooth profile 6 has a midpoint 7.

For measuring the toothing of the serrated-shaft connection, a measuringdevice 8 with a circular cross section can be used. Such a measuringdevice can be a ball or a potentiometer wire, for example.

It is advantageous if the midpoint 7 of the arc-shaped bent toothprofile 6, a point of contact 10 between a tooth 2 of the shaft 1 and atooth 5 of the hub 4, and the midpoint 11 of the measuring piece 8 lieon a straight normal line 12. As a result, the thickness of the teeth 5of the hub 4 can be exactly equal to that of the teeth 2 of the shaft 1.It is advantageous for the point of contact 10 to be located in theradial middle of the profile section.

In assembling the serrated-shaft connection, any excess material presenton the teeth 2, 5 at the points of contact is flattened so that acompressive connection that fits with great precision is obtained.

In the case of hubs having dissimilar cross sections, the shapes and/orthe bent portions of the profiles 6 of the individual teeth can bevaried to prevent nonuniform overelongation of the hub 4.

I claim:
 1. In a serrated-shaft connection between a shaft (1) having alarge number of teeth (2) on an outer circumferential surface thereofand a hub (4) having a large number of teeth located on an innercircumferential surface thereof, each tooth having a profile defined byside and top edges,the improvement which comprises the curvature of theprofile on the side edges of the shaft teeth differs from the curvatureof the profile of the side edges of the hub teeth to define first gapsbetween the tops of the shaft teeth and the hub and second gaps betweenthe tops of the hub teeth and the shaft, the first and second gaps beingdifferent to provide a precise interference fit between the hub andshaft teeth profiles.
 2. A serrated-shaft connection as defined in claim1, wherein the side edge said hub teeth profiles are bent convexly incross-section.
 3. A serrated-shaft connected as defined in claim 2,wherein the vent portion of said hub teeth profiles is a section of anarc.
 4. A serrated-shaft connected as defined in claim 2, wherein thevent portion of said hub teeth profiles has at least one point ofdiscontinuity.
 5. A serrated-shaft connected as defined in claim 2,wherein the vent portion of said hub teeth profiles have variableshapes.
 6. A serrated-shaft connected as defined in claim 4, wherein thevent portion of said hub teeth profiles have variable shapes.
 7. In aserrated-shaft connection between a shaft (1) having a large number ofteeth (2) on an outer circumferential surface thereof and a hub (4)having a large number of teeth located on an inner circumferentialsurface thereof, each tooth having a profile defined by side and topedges,the improvement which comprises the curvature of the profile onthe side edges of the shaft teeth differs from the curvature of theprofile of the side edges of the hub teeth to define a variable spacebetween adjoining hub and shaft teeth along the side edges thereof, theside edges of said hub teeth profiles being bent convexly incross-section in a section of an arc with a midpoint (7) and a point ofcontact (10) being defined between adjacent hub and shaft teeth, a linepassing through said midpoint and said point of contact also passingthrough a center (11) of a measuring device (8) having a circularcross-section used for measuring the toothing of the serrated-shaftconnection.